A conventional angle modulator is described below. FIG. 1 is a block diagram showing a configuration of the conventional angle modulator described in Patent Literature 1.
In angle modulator 10 of FIG. 1, a frequency signal input from input terminal 11 is a signal that will be frequency modulated in angle modulator 10. The frequency signal is input to adder 12, where a constant, representing information about the frequency corresponding to the center frequency of a modulated signal after modulation, is added to the frequency signal. The result of the addition in adder 12 is input to subtractor 13 and the result of frequency detection in frequency detection section 16 is subtracted from the addition result in adder 12. The result of the subtraction in subtractor 13 is input to loop filter 14, where an unnecessary signal is removed. Output of loop filter 14 is input to voltage controlled oscillator (VCO) 15, where a frequency corresponding to voltage is generated and is output from output terminal 17. Output of VCO 15 is converted into a frequency signal in frequency detection section 16.
Generally, VCO 15 can realize lower noise as current consumption is greater. Further, low noise is demanded only when output power of a transmission apparatus using angle modulator 10 of FIG. 1 is large, and therefore, low current consumption is desired when output power of the transmission apparatus is small. For this reason, as shown in FIG. 1, a configuration of switching VCO 15 to a low noise mode or a low current mode using a mode switching signal corresponding to output power of a transmission apparatus, is possible.